better support for unary plus

src/value/parse.rs

@@ -305,6 +305,10 @@ fn single_value<I: Iterator<Item = IntermediateValue>>(
                     span: op.span.merge(val.span),
                 }
             }
+            Op::Plus => {
+                devour_whitespace(iter);
+                single_value(iter, scope, super_selector, span)?
+            }
             _ => todo!(),
         },
         IntermediateValue::Whitespace => unreachable!(),

tests/subtraction.rs

@@ -199,3 +199,8 @@ test!(
     "a {\n  color: 10-#{10};\n}\n",
     "a {\n  color: 10 -10;\n}\n"
 );
+test!(
+    plus_after_minus,
+    "a {\n  plus-after-minus: 1 - + 2;\n}\n",
+    "a {\n  plus-after-minus: -1;\n}\n"
+);